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First published online July 6, 2005
Journal of Experimental Biology 208, 2719-2729 (2005)
Published by The Company of Biologists 2005
doi: 10.1242/jeb.01688

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Gene expression after freshwater transfer in gills and opercular epithelia of killifish: insight into divergent mechanisms of ion transport

Graham R. Scott^1,*, James B. Claiborne², Susan L. Edwards^2,3, Patricia M. Schulte¹ and Chris M. Wood⁴

¹ Department of Zoology, University of British Columbia, Vancouver BC, Canada V6T 1Z4
² Department of Biology, Georgia Southern University, Statesboro, GA 30460-8042, USA
³ Department of Physiology and Pharmacology, James Cook University, Cairns, QLD 4879, Australia
⁴ Department of Biology, McMaster University, Hamilton ON, Canada L8S 4K1

View larger version (16K): [in a new window]   Fig. 1. Na+,K+-ATPase activity in killifish gills (black bars) and opercular epithelium (grey bars), before (pre) and after transfer from brackish water (10% seawater) to freshwater (N=8). Values are means ± S.E.M. *Significant difference from pre-transfer brackish water control (P<0.05).

View larger version (20K): [in a new window]   Fig. 2. The estimated absolute expression levels of several genes important for ion transport in the gills (black bars) and opercular epithelium (grey bars) of killifish (N=15–20). Values are determined using Formula 1 and data are normalized to the expression level of elongation factor 1 (EF1). Na+,H+-exchanger 2 (NHE2) was not amplified above background levels in opercular epithelium. NKA, Na+,K+-ATPase 1a; VHA, V-type H+-ATPase A. #Significant difference between tissues (P<0.05).

View larger version (46K): [in a new window]   Fig. 3. Expression of genes that have similar patterns of expression between killifish gills and opercular epithelium. Na+,K+,2Cl–-cotransporter 1 (NKCC1) (A,B), cystic fibrosis transmembrane conductance regulator (CFTR) Cl– channel (C,D), and the signalling protein 14-3-3a (E,F) mRNA expression in gills (A,C,E; black/white) and opercular epithelium (B,D,F; grey) after transfer from brackish water (10% seawater) to brackish water (BW, hatched bars) or freshwater (FW, solid bars) (N=7–10). Expression is relative to the expression of EF1 and is normalized to 12 h brackish water controls. Values are means ± S.E.M. *Significant difference from time-matched brackish water control (P<0.05); significant difference from 12 h brackish water control (P<0.05).

View larger version (15K): [in a new window]   Fig. 4. Na+,H+-exchanger 2 (NHE2) mRNA expression in killifish gills after transfer from brackish water (10% seawater) to brackish water (BW, hatched bars) or freshwater (FW, black bars) (N=7–10). NHE2 is not expressed in killifish opercular epithelium. Expression is relative to the expression of EF1 and is normalized to 12 h brackish water controls. Values are means ± S.E.M. *Significant difference from time-matched brackish water control (P<0.05); significant difference from 12 h brackish water control (P<0.05).

View larger version (34K): [in a new window]   Fig. 5. Expression of genes that have different patterns of expression between gills and opercular epithelium. Carbonic anhydrase 2 (CA2) (A,B) and Na+,H+-exchanger 3 (NHE3) (C,D) mRNA expression in killifish gills (A,C; black/white) and opercular epithelium (B,D; grey) after transfer from brackish water (10% seawater) to brackish water (BW, hatched bars) or freshwater (FW, solid bars) (N=7–10). Expression is relative to the expression of EF1 and is normalized to 12 h brackish water controls. Values are means ± S.E.M. *Significant difference from time-matched brackish water control (P<0.05); significant difference from 12 h brackish water control (P<0.05).

View larger version (22K): [in a new window]   Fig. 6. Preliminary working model of Na+ absorption by killifish gills. Apical Na+ uptake occurs via NHE2 in exchange for H+ supplied by CA2. Active transport of Na+ across the basolateral surface is accomplished by Na+,K+-ATPase. Na+ may also leave the cell in symport with HCO3– through NBC1 operating in efflux mode. V-ATPase may pump H+ across the basolateral surface to help maintain intracellular acid–base balance.